Materials for dental prostheses generally consist of polymethylmethacrylate or of copolymers of different methacrylates. When a prosthesis no longer fits well, it must be manufactured afresh or relined (corrected). This relining may be effected with prosthesis material again (a hard relining) but it may also be necessary to choose a significantly softer material for such purposes (a non-hardening relining). With the average age increasing, there is a considerable rise in the demand for the last-mentioned soft materials.
Customary soft relining materials consist of polymethacrylates to which plasticiser has been added or of silicone. The polymethacrylates to which plasticiser has been added can be polymersied onto the (polymethylmethacrylate) prosthesis material, but in the course of a few months they become harder to the point of brittleness as a result of the plasticiser's dissolving out.
Relinings with silicon elastomers do not exhibit such brittleness. They remain soft over a prolonger period, but on the other hand the provision of a firm bond between silicone and polymethacrylates always presents a considerable problem. Even when attempts are made to join the layers mechanically by etching or mechanical roughening, the silicone layer becomes detached from the prosthesis after a few weeks or even after a few days.
Several methods of solving this problem by chemical means have been described. For example, DE 196 35 696 A1 describes polymers containing reactive groups, such as —OH or —NH, to which hydrogen silicone units are linked, with hydrogen being removed. Solutions of such a SiH-group-containing copolymer, after being applied to the surface of a prosthesis, are able to react with and become bonded to a vinyl silicone layer applied thereto. Since the hydrogen siloxane units are linked via —C—O—Si— or Via C—NH—Si— bonds, adhesive bonds made in accordance with this Offenlengungsschrift are extremely hydrolysis-labile in the aqueous environment of the mouth and are suitable only for short-term temporary relinings of a few days.
A better solution to the problem is described in EP 0 632 060 A1 which describes for such purposes copolymers that are prepared by copolymerisation of methylacrylates with vinyl- or allyl-methacrylates, hydrogen silicones having an adequate SiH content then being linked to the free vinyl or allyl groups with the aid of a platinum catalyst.
Solutions of such SiH-group-containing copolymers, after being applied to the surface of a prosthesis, are likewise able to react with and become bonded to a vinyl silicone layer applied thereto. The hydrogen siloxane units are linked to the polymer chain structures via ester groups —CO—O—, have better resistance to hydrolysis and are therefore effective over a longer period of time as promoters of adhesion between the material of the prosthesis and the applied silicone, even in the aqueous environment of the mouth. The preparation process is a multiple-step procedure, however, and is therefore inconvenient and expensive and the polymers prepared nevertheless have acid- and base-sensitive ester groups.